Recently, there has been a remarkably increasing requirement of a battery that can be repeatedly charged and discharged as a power source for a portable information network electronic device such as a cellular phone, a personal digital assistant (PDA), a lap top computer, and the like, a portable electronic device such as a digital camera, a camcorder, an MP3 player, and the like, or an electric bike, an electric car, and the like. A commercially-available lithium battery includes LiCoO2 at a positive electrode and carbon at a negative electrode.
However, since cobalt, a starting material of a positive active material, has a small reservoir and an environmental problem due to toxicity against a human body, an alternative positive material needs to be developed. Accordingly, there is active research on LiNiO2, LiCoxNi1-xO2, LiMn2O4, and the like as a positive active material. The LiNiO2 having the same layered structure as LiCoO2 is not yet commercially available, since it is hard to synthesize in a stoichiometric ratio and is thermally unstable. The LiMn2O4 is commercially used for some low-priced products. However, the LiMn2O4, a level 4V spinel positive active material, has an advantage of using manganese as a starting material but a structural change of Jahn-Teller distortion due to manganese 3+, resultantly bringing about a bad cycle-life characteristic.
Accordingly, a positive active material that is more economical and stable and has high capacity and an excellent cycle characteristic is required. A compound with an olivine structure has garnered attention to as a positive active material for a lithium battery. It may be represented by a Chemical Formula LixMyPO4 (herein, x is 0<x≤2, y is 0.8≤y≤1.2, and M is a transition element belonging to Group 3d in the periodic table).
Japanese Patent Laid-Open Publication Pyeung 9-171827 discloses that LiFePO4 is used for a positive electrode of a lithium ion battery among the compounds represented by LixMyPO4. LiFePO4 is environment-friendly, has an abundant reservoir, and costs very little. In addition, it may realize low electric power and low voltage more easily than a conventional positive active material. It also has theoretical capacity of 170 mAh/g and thus excellent battery capacity.
However, the LiFePO4 may not be controlled regarding particle size and shape in solid-phase reaction and wet reaction methods, in which olivine-type FePO4, the precursor of the LiFePO4, is synthesized. Thus, it may have no uniform particles. In other words, a new method of synthesizing an olivine-type positive active material suppressing a small specific surface area and having high volume energy density is required.